Destructive properties of formalin on human otoconia

Background: Formalin is a preservation media for human tissues. Since the chemical structure is known, interaction in tissue preparation can be expected, that affect otoconia morphology. To investigate the suitability of the preservation media using formalin and ethanol for human otoconia in order to prove a shortterm and long-term storage after sampling. Methods: Intact and degenerate human otoconia samples were exposed to formalin and pure ethanol. Morphological changes were observed by use of environmental scanning electron microscopy (ESEM). Results: By means of detailed environmental electron microscopy (ESEM) investigations it was shown that formalin is not a suitable storage medium for human otoconia. The solvent of the formalin solution (H2O) attacks the calcite component of human otoconia immediately after exposure. At the same time the organic components of otoconia (proteins) are stabilized by interaction with formaldehyde and their original structure remains unaffected. After ethanol exposure, the morphology of otoconia remains unchanged. Conclusions: Formalin is not suitable for preservation of tissue material containing otoconia if further ultrastructural and morphological investigations should be performed. A suitable medium for preserving otoconia is pure ethanol, which keeps the composite structure without morphological changes over a long period of time.